Importance of understanding performance requirements of UPVC products, before starting production

Introduction:

ISO 9001:2015 demands that before accepting the order, a review must be carried out regarding –

1)????Requirements specified by the customer – Most purchase orders will demand pipe meeting IS 4985:2021 or other relevant standard requirements in their purchase order.

2)????Requirements not stated by the customer but necessary for the specified or the intended use, where known – Like whether the pipe will be installed in certain severe conditions.

3)????And, whether the organization is capable of meeting these requirements.

Usually, customer purchase order demands that the pipe quality should conform to the requirements of IS 4985:2021 or any other relevant standard.

Impact strength is the most important test, even though the pipe for potable water supply is marked with the pressure rating. Some QA people feel that pressure test is more important as it is a pressure pipe as compared to impact test at 0? C. As a result, the pipe may fail during actual use.

The reasons are –

1.?????Pipes are tested not for its actual impact strength, but to ensure that it withstands the minimum impact energy at 0? C, as per IS 4985:2021.

2.?????10% failure is accepted in this test. Question is why not 0% failure?

3.?????Though the pipe is tested along the circumference, the weakest points corresponding to impact strength might get escaped during the impact test. These weaker points along the circumference might be due to uneven fusion, uneven temperatures at the die, uneven cooling or uneven reversion.

4.?????In summer the ambient temperature may be 45? C, the test sample might increase its temperature within 10-20 seconds, if the ambient temperature in the test lab is not maintained at 27+/-1? C+.

5.?????The pipes are stacked in an open yard, either at the manufacturer’s place or at customer’s place. Due to ageing process (annealing in the hot atmospheric conditions), the impact strength reduces. The 10% failure may get magnified in such cases.

6.?????UV degradation also causes reduction in impact strength.

A case study:

In one organization, pipes were supplied to the customer through a distributor. In distributor purchase order, the quality requirements were - conforming to IS 4985:2021 standard.

The pipes were genuinely passing in all the tests as per IS 4985 2021, including the impact test.

The distributor supplied some pipes from the same lot to the hot region and others to very cold region.

The organization received a complaint and the pictures from the customer in the cold region through the distributer that the pipes are breaking.

The organization took a stand that since the pipes were passing in all the tests including the impact test at 0? C, this cannot be a quality problem. The organization thought that probably, either the distributor or the customer wants to delay the payment.

Resolving this issue through replacement of the pipes was ruled out by the organization.

The why-why analysis to find the root cause:

1.?????Why the UPVC pipes genuinely passing in all the tests broke in cold region and not in the hot region?

Because the ambient temperature was very low in the cold region and pipes become brittle.

2.?????Why the pipes displayed brittleness in the cold region?

Because, the ambient temperature was below the brittleness temperature (Tb) of the pipe, hence impact strength reduced.

3.?????Why the Tb of the pipe was more than the ambient temperature?

Because, impact modifier was not added in the formulation.

4.?????Why addition of impact modifier was not considered?

Because the performance requirement that the pipe will be installed at zero or sub-zero temperature was not known.

5.?????Why the performance requirement was not known?

Because, the performance requirement point is not included in the customer requirement review format, hence as per the stated requirements, the pipes conforming to IS 4985:2021 were supplied, without clarifying from the distributor – An immediate customer. (Root cause)

Corrective actions:

a.?????The review format was revised to include a point related to performance requirement.

b.?????Training calendar was modified to include training on review of customer requirements for staff in sales and marketing, PPC as well as QA departments.

c.?????All distributors were informed to mention specific performance requirements for their customers, if any. In case of no specific requirements, the distributor should mention – Nil.

d.?????Sales and marketing people were informed to to ask the distributor and record performance?requirements in the review document and if they need any help for clarification.

e.?????The increased prices for impact modified UPVC pipes for specific requirements were informed to the distributors.